<div dir="ltr"><div>- Gerald,</div>
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<div>I agree with your comments. </div>
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<div>In regard to my comment on Dr. Schmunk -- he mentioned his research to me during conversations he and I had when discussing various formulas and reference material I have for use with his 'G.Projector' software. If he is still monitoring 'Proj' he may respond to our discussion, or you could ask him via an e-mail about this.</div>
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<div>- Paul<br></div>
<div class="gmail_quote">On Sat, Sep 13, 2008 at 1:40 PM, Gerald I. Evenden <span dir="ltr"><<a href="mailto:geraldi.evenden@gmail.com">geraldi.evenden@gmail.com</a>></span> wrote:<br>
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<div class="Wj3C7c">On Saturday 13 September 2008 12:26:58 pm Paul B. Anderson wrote:<br>> - Janne,<br>><br>> The difficulty comes about because the Tripel is actually composed of 2 map<br>> projections -- the Aitoff (pronounced 'I-toff') projection averaged with<br>
> the Equirectangular projection (which provides the Special Parallel input).<br>> Yes, there are inverse formulas out there for the Tripel, but the values<br>> produced are approximations.<br>><br>> One person who has researched the inverse Winkel Tripel formulas issue is<br>
> Dr. Robert Schmunk <a target="_blank" href="http://www.giss.nasa.gov/staff/rschmunk.html">http://www.giss.nasa.gov/staff/rschmunk.html</a><br>><br>> BTW, a reference for this map projection is Snyder's 'Flattening the<br>
> Earth'.<br>><br>> Paul B. Anderson FCCS (USN, Retired)<br>> Kingsport, TN native living in Norfolk, VA<br>> My Map Projection web site:<br>> <a target="_blank" href="http://www.csiss.org/map-projections/index.html">http://www.csiss.org/map-projections/index.html</a><br>
><br>> ----- Original Message -----<br>> From: <<a target="_blank" href="http://support.mn/">support.mn</a>@<a target="_blank" href="http://elisanet.fi/">elisanet.fi</a>><br>> To: "PROJ.4 and general Projections Discussions" <<a href="mailto:proj@lists.maptools.org">proj@lists.maptools.org</a>>;<br>
> <<a href="mailto:geraldi.evenden@gmail.com">geraldi.evenden@gmail.com</a>><br>> Sent: Saturday, September 13, 2008 11:42 AM<br>> Subject: Re: [Proj] Unknown projection?<br>><br>> > "Gerald I. Evenden" <<a href="mailto:geraldi.evenden@gmail.com">geraldi.evenden@gmail.com</a>> kirjoitti:<br>
> >> On Saturday 13 September 2008 10:59:24 am Paul B. Anderson wrote:<br>> >> > - Janne,<br>> >> ><br>> >> > Your map graphic appears to be in the Winkel Tripel map projection. I<br>
> >> > would<br>> >> > also suggest that it is using Oswald Winkel's original selection of<br>> >> > 50.46667 degrees as the Special Parallel.<br>> >> ><br>> >> > Note that by the 1950s John Bartholomew was using a special parallel<br>
> >> > of 40<br>> >> > degrees for his version of the Tripel, giving his graphic a more<br>> >> > flattened<br>> >> > appearance in the Y direction.<br>> >><br>> >> This is exactly why I include the projection math in the manual. The<br>
> >> factor Anderson is discussing is +lat_1 option for the +proj=wintri<br>> >> projection. Select your own option value and name a new projection.<br>> >> ;-)<br>> ><br>> > Ok, now the problem seems to be that "wintri" does not have any inverse<br>
> > projection<br>> > available. What is the reason not to have inverse projections for all<br>> > routines<br>> > in the library... math is too hard?<br>> ><br>> > Janne.<br><br></div>
</div>I can't find any reference on his website to research on Winkel Tripel so I<br>suspect he has not published it.<br><br>I take back my comment on ease of solution but it would seem to be invertible<br>using iterative techniques---but slow. Accuracy should only be dependent<br>
upon how many cpu ticks you want to give it.<br>
<div class="Ih2E3d"><br>--<br>The whole religious complexion of the modern world is due<br>to the absence from Jerusalem of a lunatic asylum.<br>-- Havelock Ellis (1859-1939) British psychologist<br>_______________________________________________<br>
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